Upgrading from 23.10 to 24.04 LTS

But LinuxMint has Ubuntu 22.04 as "background"... I'd never turn back to Ubuntu 22.04... thinking of the improvements in later Ubuntu ( > 22.04) versisons.

Have an office PC running LinuxMint (latest stable) with MATE desktop enviroment => ok
Have my daily rig (Home PC) running Ubuntu MATE 24.04 - fresh install => perfect

NOTE: Do not upgrade to Ubuntu (any flavor) 24.04. Wait until the upgrade is officially supported. If you still want to upgrade, a fresh install will be the solution to go for. See my comment here